IntelliJ IDEA 2016.1 Help

Runner

Platform Test Runner - select this option if you want to run your tests using the
IntelliJ IDEA API.

Gradle Test Runner - select this option if you want to run your tests using
Gradle tooling API.

Let me choose per test - select this option if you want to choose the
runner for the specific test.
In this case IntelliJ IDEA prompts you to select the test runner the first time you try to execute
your test.